Reinforcement fibers are used in a variety of products. The fibers can be used as reinforcements in products such as plastic matrices, reinforced paper and tape, and woven products. During the fiber forming and collecting process, numerous fibers are bundled together as a strand. Several strands can be gathered together to form a fiber bundle used to reinforce a polymer matrix to provide structural support to products, such as molded plastic products. The strands can also be woven to form a fabric, or can be collected in a pattern as a fabric.
Reinforcing glass strands are conventionally prepared by mechanically drawing molten glass streams flowing by gravity from multiple orifices of bushings filled with molten glass to form filaments which are gathered together into base strands, and then collected. During the drawing of the glass filaments, and before they are gathered together into strands, the glass filaments are often coated with a sizing composition, generally an aqueous sizing composition, using a rotating roller. The sizing composition (also referred to as “size”) is traditionally applied during manufacture of the glass filaments to protect the filaments from the abrasion resulting from the rubbing of the filaments at high speed during the forming and subsequent processes, thus acting as lubricant. It also makes it possible to remove or avoid electrostatic charges generated during this rubbing. Additionally, during the production of reinforced composite materials, the size improves the wetting of the glass and the impregnation of the strand by the material to be reinforced.
After the reinforcing fibers are produced, they are frequently processed on looms or other weaving devices to produce woven fabrics. The weaving process traditionally includes both warp yarns, which are the lengthwise or longitudinal yarns, and weft yarns, which transverse the warp yarns and are traditionally inserted over-and-under the warp threads, acting as filler. However, the crimping of the yarns that occurs as the warp and weft yarns cross over and under each other reduces the tensile and the compressive strength of a woven fabric. Additionally, the weft yarns add weight without providing significant additional benefits to the physical properties.
Unidirectional fabrics are fabrics with at least approximately 80% of the total fibers in a single direction, generally in the warp direction, also known as the load direction of the laminate. Accordingly, if a unidirectional fabric includes weft fibers, they generally account for less than 20% of the total fibers in the fabric and provide a backing structure to allow for the knitting/stitching of the fabric, thus providing a stable textile structure.
Weft fibers have traditionally been a necessary component in fabrics, acting as a stabilizer to mechanically bind the unidirectional fiber bundles as a backing and to maintain a distance between the unidirectional fibers, thus generating channels for resin impregnation in vacuum infusion processing. For instance, applications such as the production of wind turbine blades traditionally employ fiber bundles in various orientations that are stitched together, forming a preform. Such preforms include weft fibers that act as a carrier for the load bearing fibers, holding the preform together. The quality of wind turbine blades is determined, at least in part, by both the fatigue in relation to the lifetime of the blade and also the stiffness of the blade. However, weft fibers in a unidirectional laminate have shown to cause increased fatigue and also stiffness degradations over the lifetime of the blade.